TA bufferes initialize

[Twada]

Hello.

I'm trying to make an TA bufferes initialize by reference to the Marcus's sample.
I wouid like to use Texture freely and lerge in VRAM. So I would like to put the TA buffer at the bottom of the VRAM.
However, if the bottom address(TA_BUFFER_BOTTOM2) of the Ta buffer is 0xa5800000, the screen freezes.
but if the adress is 0xa5700000, not freezes.

Code: Select all

#define TA_BUFFER_BOTTOM1	0xa5400000
#define TA_BUFFER_BOTTOM2	0xa5800000

/* TA Buffers */
static unsigned char *vtx_buf[2];              /* Vertex CMD buffer*/
static unsigned char *obj_ptr_buf[2];        /*Object pointer buffer*/
static unsigned char *tile_buf[2];              /*Tile buffer*/
static unsigned char *screen[2];               /*screen*/

static int current;   /*video flip num*/
static int scr_w;     /*screen width*/
static int scr_h;     /*screen height*/
.........
.........
void ta_create_buffer(){
	int i;
	unsigned char *ptr = (unsigned char *)TA_BUFFER_BOTTOM1;
	int h = scr_w>>5;            /*Tile num*/
	int v = scr_h>>5;
		
	for (i = 0; i<2; i++, ptr = (unsigned char *)TA_BUFFER_BOTTOM2) {
		ptr -= scr_w * scr_h * 2;
		screen[i] = ptr;

		ptr -= ((24 + (6 * h*v)) * 4);
		tile_buf[i] = ptr;                 /*Tile Buffer*/
		
		ptr -= (512 * 1024);
		vtx_buf[i] = ptr;                  /* Vertex Buffer */
		
		ptr -= (128 * h*v * 3);            /*(128*w*h) * (opaque+transparent+punchthruの分) */
		obj_ptr_buf[i] = ptr;              /*Object Pointer Buffer*/
		
		/*set tile buffers*/
		ta_create_tile_buffer(tile_buf[i], obj_ptr_buf[i], h, v);
	}
}

The following registry is set. I do not know the cause. Help me.

Code: Select all

volatile unsigned int *regs = (volatile unsigned int *)0xa05f8000;
unsigned int vtx = ( (unsigned int)(vtx_buf[current]) )&0x007fffff;
unsigned int opb = ( (unsigned int)(obj_ptr_buf[current]) )&0x007fffff;

        regs[0x008/4] = 1;		                                 /* Reset TA */
	regs[0x008/4] = 0;
	regs[0x124/4] = opb;
	regs[0x12c/4] = 0;
	regs[0x128/4] = vtx;
	regs[0x130/4] = vtx + (512*1024);
	regs[0x13c/4] = (((scr_h>>5)-1)<<16) | ((scr_w>>5)-1);
	regs[0x164/4] = opb;
	regs[0x140/4] = 0x00130303;
	regs[0x144/4] = 0x80000000;

[bogglez]

Aren't you writing past the second VRAM bank there? What happens if you lower the value to 0xa57ffffc or below? In my code I have these numbers:

Code: Select all

static volatile union ak_pointer vram_bank1     = { .as_u8 = (u8*)0xa5000000 };
static volatile union ak_pointer vram_bank2     = { .as_u8 = (u8*)0xa5400000 };
static const   union ak_pointer vram_bank1_end = { .as_u8 = (u8*)0xa53ffffc };
static const   union ak_pointer vram_bank2_end = { .as_u8 = (u8*)0xa57ffffc };

[Twada]

Thank you for your comment!
I tried some low addresses. However, the Dreamcast was frozen.

I noticed that this cause is in 0xa05f808c register.

Code: Select all

unsigned int vtx = ( (unsigned int)(vtx_buf[current]) )&0x007fffff;
unsigned int *taend = (unsigned int *)(void *)(0xa5000000|regs[0x138/4]);
......
regs[0x08c/4] = 0x01000000 | ((((char *)taend)-((char *)vtx))<<1);   /*bg plane*/

When commenting out this register, it did not freeze.
I think this register is for BG Plane. I don't know why to set vertex cmd address in this register.